I would start by cleaning- if the burner and/or orifice is dirty, when it goes to low flame, the flame will be too small. IIRC, the 46E was the new style cooling unit and burner, so I would soak the orifice in alcohol and air dry, clean the burner. Another issue with some of those old models is there is an LP filter in the line. After all these years, the filter gets clogged. I think it is removable on most models, but not sure.
The ignitor should be the piezo type, and it should snap when pushed, producing a spark. If it does snap but doesn't work, it's probably shorted somewhere.
I have a couple of service manuals that should help- the
non electronic model diagnostic manual, and the
older RM manual- the older one has the RM46, just not the E, so much is different.